Process of preparing plastic coated high explosive particles and articles



United States ate ABSTRAQT OF THE DISCLQSURE This invention is a process of preparing explosives, cyclotrimethylenetrinitramine, for example, in a plastic material capable of being set or formed to various shapes. The plastic material, such as rubber, is dissolved in a solvent, added to a non-solvent emulsifying liquid, and the high explosive particles added. The particles can be recovered as separate, coated particles or pressed into a shaped article.

This application is a division of application Ser. No. 486,306 filed Feb. 4, 1955.

This invention relates to high explosives and more particularly to high explosives bonded by elastomeric materials.

It is necessary for certain uses of high explosives to have the explosive material in a plastic form capable of being set or formed to various shapes. Such shapes may be formed permanently or altered at will. Thus, it may be desirable, for example, to have an explosive which can be made to adhere to the side of an item. Pliable or moldable explosive-type compounds have been made by incorporating mineral oil or similar liquid hydrocarbons containing a small percentage of a binder, into an explosive composition. Although the consistency of such a mixture could be varied to some extent, the form in which it could be used was limited by the fact that such pliable compositions could not be made into permanently shaped forms nor could they be used at temperatures below which the mineral oil became too stiff or solidified.

I have found that explosive compositions bonded by an elastomeric material can be made in a large number of forms ranging from very soft pliable material to hard moldable material which is capable of maintaining permanent configurations. In addition, the explosive materials formed by this invention may have rubber-like qualities, i.e., they may be made to rebound, to stretch and pull. Since these elastomer bonded explosives are formed by first coating explosives particles with the elastomeric materials, the process of this invention also serves as means of desensitizing explosives, a very important step in handling highly explosive materials.

It is, therefore, an object of this invention to make an explosive with rubber-like properties. It is another object of this invention to make explosive compositions which are vulcanizable and which hold their structure. It is still another object of this invention to make explosives which are pliable and capable of being worked into any desired shape. It is a further object of this invention to make an explosive which is capable of adhering to a material such as wood, metal, plastics, etc. It is still a further object of this invention to make a flexible explosive which will remain flexible at low temperatures. It is yet another object of this invention to desensitize explosives. These and other objects will become apparent in the discussion to follow.

Elastomeric materials such as rubber (whether synthetic, natural or of the silicone type) are normally compounded with one or more fillers and one or more modifying agents such as anti-oxidants, vulcanizers, etc. However, the usual method of compounding rubber by milling ice cannot be safely employed in making an elastomer bonded explosive containing more than 70 percent explosive by weight since the shearing action of a rubber mill or Banbury mixer is too great with respect to the sensitivity of the explosive to allow the addition of such a large quantity of the explosive to be incorporated into the rubber safely. In addition, the heat produced during the milling operation is not tolerable in an explosives compounding process involving a large amount of explosive. Thus, the usual method of compounding rubber-like materials can be employed for making small batches of elastomer-bonded explosives of low explosive content, but it is not preferred from a safety point of view. a a a Because of the dangers inherent in into the elastomeric material by methods commonly used with other fillers, it was necessary to develop alternative, safer, procedures for making the elastomer-bonded explosives of this invention. These methods have been designated the solvent and latex methods. The elastomeric material, either in solution or as a latex, is introduced into an emulsifying medium along with additives, one or more fillers if desired and the high explosive. The elastomeric material is then partially or completely cured or vulcanized in the emulsifying medium. In this manner the explosive is coated and bonded by the elastomeric material. The elastomer bonded explosive is removed from the emulsifying medium, dried, formed into desired shapes, and further cured if necessary. If elastomer-coated explosives particles are desired, molding or further pressing is not necessary. The elastomer coating may or may not be further cured, depending upon the characteristic sought in the final coated particles.

In the solvent method, the elastomer is dissolved in a suitable solvent along with any compounding agents (accelerators, vulcanizing agents, pigments, stabilizers, etc.). This solution is stirred into an emulsifying liquid medium which is a non-solvent for the elastomer and the high explosive, and which is essentially immiscible with the elastomer solvent. A stabilizer may have been added to the emulsifying liquid medium before adding the elastomer solution. The resulting emulsion is stirred until discrete spheres of the elastomer are formed, and then the high explosion, of graded size, along with any filler, is introduced into the emulsifying liquid medium. Stirring is continued until the explosive granules are coated by coagulation of the elastomeric material on the explosive and elastomer-explosive sphere-like particles are formed. During the mixing process or after the elastomer-explosive particles are formed, heat is applied to partially or completely cure the elastomeric material, if so desired, and finally to drive off the solvent used to put the elastomer material in solution. A convenient way to apply the heat required is to bubble steam through the emulsifying liquid medium. The elastomer-explosive particles are filtered from the emulsifying liquid medium, dried and if desired, pressed into forms or shapes or extruded or calendered and further cured if necessary.

The latex method is begun with a stabilized latex of the elastomer to which any other desired additives have been added. The particles of explosives material are added to the latex and the mixture is stirred while the latex is being c-oagulated on the explosives particles. Stirring and coagulation must be so regulated that agglomerates are not formed but that discrete coated particles come down in the liquid medium. The coagulation of the elastomeric material may be induced by heat or by the addition of a coagulating agent such as sodium silicofluoride or an acid such as acetic acid. If coagulation is accomplished by means of heat the heat may be conveniently applied by various means but is preferably applied by passing steam through the emulsifying liquid medium. A filler may be introduced in the latex or along with the milling the explosive explosives particles. If the elastomer is to be cured while the elastomer coated explosive is suspended in the emulsifying liquid medium, heat is applied until the desired degree of curing is accomplished. After the elastomerc-oated explosive granules are separated from the emulsifying liquid medium, they are dried to complete the removal of the emulsifying liquid medium. Depending upon the product desired, the elastomer bonded explosive is transferred to a mold, die, extruder or calender for fabrication and the article formed is cured further if necessary. If coated, desensitized explosive particles are desired, the fabrication steps are omitted.

The high explosive to be so bonded may be any of the well known explosive materials which are compatible with the elastomeric material and which are not soluble in the emulsifying liquid medium suitable for the coating ,7

and coagulating processes. Such explosives include but are not limited to cyclotrimethylenetrinitramine, cyclotetramet-hylenetetranitramine, pentaerythritol tetranitrate, bis (trinitroethyl) nitramine, bis(trinitroethyl) urea and ammonium perchlorate. The minimum percentage of explosive which can be compounded into the rubber is determined by the amount of explosive required to make the final product detonate. The maximum amount of explosive is determined by the bonding power of the elastomer and the amount of flexibility desired. Thus, below about 80 percent explosive, by total weight, it is difficult to detonate an elastomer bonded explosive unless a booster is used, while above about 95 percent explosive, the clastomer bonded explosive becomes too stiff and inflexible, there is a tendency for the explosive to flake out and the material becomes too sensitive to handle. The weight range of explosive is between 50 and 95 percent by weight while the preferable range for an easily detonable explosive is between 85 and 90 percent.

The elastomeric material used may be natural or synthetic rubber or silicone rubber, the type used determining the modifying agents which should be added to it. Such modifying agents will be illustrated in the examples below. The amount of vulcanization agents will be determined by the degree of pliability, flexibility and hardness desired in the final elastomer bonded explosive.

The solvent used for making up the elastomer solution may be any liquid which is a solvent for the elastomer used and which is substantially immiscible with the emulsifying liquid medium used as a vehicle for the coating and coagulating processes. Such solvents as carbon tetrachloride, benzene, toluene, and ethylene dichloride may be used. Carbon tetrachloride has been found to be one of the most satisfactory solvents. I-t is desirable to keep the amount of solvent to a workable minimum to make final solvent removal easier and faster.

The non-solvent liquid used to make a latex or as the emulsifying liquid agent should preferably be a liquid which is inexpensive, and easily and safely handled. It must, of course, be a non-solvent for the elastomeric material and the high explosive used.

As pointed out above, fillers may be added to the elastomer bonded materials. Such fillers are preferably materials which contribute to the performance of the explosive, such as a metal, and which do not render the explosive insensitive to final detonation. Although the character of the filler will determine the optimum amount to be used, quantities up to 30 to 35 percent by total weight are feasible.

The following examples are given to illustrate the procedures of this invention without, however, limiting its scope.

Example I In a three-liter Morton flask containing 300 ml. of water and 0.8 ml. of a liquid soap as a wetting agent was added a carbon tetrachloride solution of 2.4 grams of rubber (containing 2.5 percent sulfur and percent zinc oxide) with high speed stirring. When the rubber was fully dispersed, 9 grams of ultra-fine cyclotrimethylenetrinitramine was added to the dispersion. Stirring was continued until all of the cyclotrimethylenetrinitramine was coated by the rubber (in about 15 to 20 minutes). Then 0.2 gram of Butyl-8 catalyst (water solution of sodium dibutyldithiocarbamate) was added. The reaction vessel was immersed in hot water and vacuum applied to remove the carbon tetrachloride. The reaction vessel was removed from the hot water and the rubberized material removed by filtration. The small discrete, slightly tacky particles were air dried for 3 hours, then placed in a mold and pressed at 1000 psi. The pellets, after removal from the mold, were placed in an oven at C. for 3 hours for complete cure. The percentage composition of the final rubberized explosive was 79 percent cyclotrimethylenetrinitramine and 21 percent rubber. The material had a Shore hardness A 40-50 and was rubbery and flexible.

Example II Following the same procedure as set forth in Example I above, 2-5 grams of a rubber solution (containing 3.5 grams of solids composed of 92.5 percent rubber, 5 percent zinc oxide accelerator, 2.5 percent sulfur) 74 grams of ultra-fine cyclotrimethylenetrinitramine, and 0.1 gram Butyl-8 catalyst were dispersed in water. Heat was applied as in Example I and a vacuum maintained until substantially all of the carbon tetrachloride was removed. The rubberized explosive material obtained from this batch was partially cured. On pressing some of this material into a wafer of approximately 2" diameter and /2" thickness a hard, smooth surface was obtained which felt rubbery. The material, which contained 95.5 percent explosive, was frangible.

Example III Following the same procedure as set forth in Example I above, 25 grams of rubber solution (containing 3.5 grams of solids composed of 92. 5 percent rubber, 5 percent zinc oxide and 2.5 percent sulfur) and 0.2 ml. of a liquid soap as a wetting agent were dispersed in 300 ml. of water. Then 0.5 gram of Cabot-Monarch 71 carbon black was added and when all of the components were fully dispersed, 17.5 grams of ultra-fine cyclotrimethylenetrinitramine was added. Finally 0.2 gram of Butyl-8 catalyst was added. Heat was applied by passing steam through the liquid for one and one half hours. The rubberized explosive was collected on a filter and air dried. It was completely cured, black in color, rubbery and contained 81.5 percent high explosive.

Example IV Three hundred and six grams of a GRAS synthetic rubber solution in carbon tetrachloride (containing 41.3 grams of solids composed of 93 percent GR-S, 5 percent zinc oxide accelerator and 2 percent sulfur) was added to water and dispersed with liquid soap as a wetting agent. Ultra-fine cyclotrimethylenetrinitramine in the amount of 206 grams, 3.0 grams of Cabot-Monarch 71 carbon black, and 0.8 gram of Butyl-8 catalyst were added and heat applied by stream injection for one-half hour. The rubber-coated material was removed from the dispersion and air dried. Pellets pressed from the resulting material were cured in an oven at 80 C. for three hours. The final product, containing 82.3 percent cyclotrimethylenetrinitramine, had rubber-like properties.

Example V In a five-liter Morton flask containing 2 liters of water and 0.5 gram of gelatin, as a stabilizer, there were added 132.2 grams of a carbon tetrachloride rubber solution (containing 17.2 grams of rubber solids, and sulfur, zinc oxide and Age-Rite powder (phenol-B-naphthylamine) in the ratio of 3/5/0.5 parts per parts of rubber), grams of cyclotrimethylenetrinitramine, and 0.69 gram of Butyl-8. Steam was injected into the mixture for about seven minutes and then cold water was added to reduce the temperature to about 50 C. The rubber coated particles were filtered from the liquid and were further washed and dried. The material was pressed into a cylinder OD. x 3.4" high and had a density of 1.63 grams/cc.

Example VI Compounding ingredients consisting of 1.5 grams zinc oxide, 0.3 gram sulfur and 0.3 gram bis(2-hydroxy-3- tertiary-butyl5-methyl) methane as an antioxidant were dispersed by ball milling in a small amount of water containing about 1 to 2% Triton X-lOO (a wetting agent) and adjusted to a pH of to 10.5. This dispersion was added to 60 grams of Neoprene latex containing 30 grams of Neoprene by weight, and the resulting mixture added to two liters of water containing 0.5% gelatin and sufficient ammonium hydroxide to adjust the water to a pH of 10 to 10.5. To this was also added 0.3 gram activated dithiocarbamate and 0.30 gram tetraethylthiuram disulfide as accelerators. The entire mixture was stirred for about minutes and then 85 grams of cyclotrimethylenetrinitramine was added and stirring continued for minutes more. At the end of this stirring period acetic acid was added to induce the coagulation of the latex. Steam was passed through the mixture for about 40 minutes and then the resulting mass was filtered, washed with water and air dried. After pressing the material to the desired shapes, the articles were finally cured. The resulting elastomer bonded explosive contained 85% explosive by weight.

Four other compositions were made up by the abovedescribed latex method to form elastomer bonded explosives With the characteristics described herein. These were as follows:

Composition A Grams Hycar latex 73 Zinc oxide 0.6 Sulfur 0.6 Activated dithiocarbamate 0.9 Zinc dibutyldithiocarbamate 0.3 Cyclotrimethylenetrinitramine 183 1 grams rubber.

Composition B Natural rubber latex 50 Zinc oxide 0.9 Sulfur 0.6 Activated dithiocarbamate 0.6 Bis(2-hydroxy-3-tertiary butyl-S-methyl) methane 0.3

Cyclotrimethylenetrinitramine 183 1 30 grams rubber.

Composition C Kralac latex 48.4 Zinc oxide 0.9 Sulfur 0.45 Activated dithiocarbamate 0.9 Benzothiazyl disulfide 0.3

Bis(2-hydroxy-3-tertiary butyl-S-methyl) methane 0.3

Cyclotrimethylenetrinitramine 186 1 30 grams rubber.

Composition D Natural rubber latex 1 50 Zinc oxide 0.9 Sulfur 0.6 Activated dithiocarbamate 0.6

Bis(2-hydroxy-3-tertiary butyl-S-methyl) methane 0.3 Cyclotetramethylenetetranitramine 183 1 30 grams rubber.

From the discussion and examples it is seen that it is possible by means of this invention to prepare elastomerbonded explosives which can be formed into any desirable shape, and which can be made flexible and pliable or to any consistency desired.

Having described my invention, what I claim is:

1. A process for making an elastomer-bonded explosive which comprises forming a solution of an elastomer in a solvent, adding the resulting elastomer solution to a non-solvent emulsifying liquid agent, mixing in high explosive particles and the necessary elastomer modifiers, agitating the resulting liquid mixture until the high explosive particles are coated, said elastomer, removing the resulting elastomer-coated explosive particles, and drying said elastomer-coated explosive particles, said high explosive being present in a concentration from about 50 to percent by weight, said solvent being a nonsolvent for said high explosive, said emulsifying liquid medium being a non-solvent for the elastomer and the high explosive.

2. A process for making an elastomer-bonded explosive which comprises forming a solution of an elastomer in a solvent, adding the resulting elastomer solution to a nonsolvent emulsifying liquid agent, mixing in high explosive particles and the necessary elastomer modifiers, agitating the resulting liquid mixture at an elevated temperature until the high explosive particles are coated and the elastomer coagulatcd and partially cured, removing the resulting elastomer-coated explosive particles, drying said elastomer-coated explosive particles, fabricating them into the desired shape, and completing the curing of the resulting elastomer-bonded explosive articles, said high explosive being present in a concentration from about 50 to 95 percent by weight, said solvent being a non solvent for said high explosive, said emulsifying liquid medium being a non-solvent for the elastomer and the high explosive.

3. A process in accordance with claim 2 wherein the elevated temperature is attained by steam injection.

4. A process for making an elastomer-bonded explosive which comprises adding high explosive particles and elastomer modifiers to the latex of an elastomer, agitating the resulting liquid mixture and causing latex to coagulate on the high explosive particles to coat them with said elastomer, removing the resulting elastomer-coated explosive particles, drying said elastomer-coated explosive particles, said high explosive being present in a concentration from about 50 to 95 percent by weight, said nonsolvent being a non-solvent for said high explosive.

5. A process for making an elastomer-bonded explosive which comprises adding high explosive particles and elastomer modifiers to the latex of an elastomer, agitating the resulting liquid mixture at an elevated temperature until the high explosive particles are coated with said elastomer and the elastomer coagulated and partially cured, removing the resulting elastomer-coated explosive particles, drying said elastomer-coated explosive particles, fabricating them into the desired shape, and completing the curing of the resulting elastomer-bonded explosive article, said high explosive being present in a concentration from about 50 to 95 percent by weight, said nonsolvent being a non-solvent for said high explosive.

6. A process in accordance with claim 5 wherein the elevated temperature is attained by steam injection.

7. A process for making rubber-bonded cyclotrimethylenetrinitramine which comprises forming a solution of rubber in carbon tetrachloride, adding the resulting solution to water, mixing in said cyclotrimethylenetrinitramine and the necessary rubber modifiers, agitating the mixture at an elevated temperature until the cyclotrimethylenetrinitramine particles are coated with said rubber and the desired degree of vulcanization of said rubber is attained, removing the resulting rubber-coated cyclotrimethylenetrinitramine particles, drying and fabricating said rubber-coated cyclotrimethylenetrinitramine, and curing the resulting fabricated rubber-coated cyclotrimethylenetrinitramine, said cyclotrimethylenetrinitramine being present in a concentration from about 70 to 90 percent by Weight.

8. Aprocess in accordance with claim 7 wherein the elevated temperature is attained by steam injection.

9. A process for making rubber-coated cyclotrimethylenetrinitrarnine which comprises adding cyclotrirnethylenetrinitramine particles and rubber modifiers to a rubber latex, agitating the resulting liquid mixture at elevated temperatures and causing the latex to coagulate on the said cyclotrimethylenetrinitramine particles to coat them with said rubber, removing the resulting rubber-coated cyclotrimethylenetrinitramine particles, drying and fabricating said rubber-coated cyclotrimethylenetrinitramine and curing resulting fabricated rubber-bonded cyclotrimethylenetrinitrarnine article, said cyclotrimethylenetrinitramine being present in a concentration from about 70 to 90 percent by Weight.

10. A process for making rubber-bonded cyclotetramethylenetranitramine which comprises forming a solution of rubber in carbon tetrachloride, adding the resulting solution to water, mixing in said cyclotetramethylenetetranitramine and the necessary rubber modifiers, agitating the mixture at an elevated temperature until the cyclotetramethylenetetranitramine particles are coated with said rubber and the desired degree of vulcanization of said rubber is attained, removing the resulting rubbercoated cyclotetramethylenetetranitramine particles, drying and fabricating said rubber-coated cyclotetramethylenetranitrarnine and curing the resulting fabricated rubber-coated cyclotetramethylenetetranitramine, said cyclotetramethylenetetranitramine being present in a concentration from about 70 to 90 percent by weight.

11. A process for making rubber-coated cyclotetra methylenetetranitramine which comprises adding cyclotetramethylenetetranitramine particles and rubber modifiers to a rubber latex, agitating the resulting liquid mixture at elevated temperatures and causing the latex to coagulate on the said cyclotetramethylenetetranitrarnine particles to coat them with said rubber, removing the resulting rubber-coated cyclotetramethylenetetranitramine particles, drying and fabricating said rubber coated cyclotetramethylenetetranitrarnine and curing resulting fabricated rubber-bonded cyclotetramethylenetetranitramine article, said cyclotetramethylenetetranitramine being present in a concentration from about 70 to 90 percent by weight.

References Cited UNITED STATES PATENTS BENJAMIN R. PADGETT, Primary Examiner. 

1. A PROCESS FOR MAKING AN ELASTOMER-BONDED EXPLOSIVE WHICH COMPRISES FORMING A SOLUTION OF AN ELASTOMER IN A SOLVENT, ADDING THE RESULTING ELASTOMER SOLUTION TO A NON-SOLVENT EMULSIFYING LIQUID AGENT, MIXING IN HIGH EXPOSIVE PARTICLES AND THE NECESSARY ELASTOMER MODIFIERS, AGITATING THE RESULTING LIQUID MIXTURE UNTIL THE HIGH EXPLOSIVE PARTICLES ARE COATED, SAID ELASTOMER, REMOVING THE RESULTING ELASTOMER-COATED EXPOLOSIVE PARTICLES, AND DRYING SAID ELASTOMER-COATED EXPLOSIVE PARTICLES, SAID HIGH EXPLOSIVE BEING PRESENT IN A CONCENTRATION FROM ABOUT 50 TO 95 PERCENT BY WEIGHT, SAID SOLVENT BEING A NONSOLVENT FOR SAID HIGH EXPLOSIVE, SAID EMULSIFYING LIQUID MEDIUM BEING A NON-SOLVENT FOR THE ELASTOMER AND THE HIGH EXPLOSIVE. 